Synthesize a minimum of forty of the proposed LHRH antagonists in 10 mg. quantities. Synthesize related LHRH antagonists. Synthesize selected antagonists in adequate quantities to conduct additional antiovulatory testing. Measure the partition coefficients of selected potent, hydrophobic analogs and correlate this with the analogs' subcutaneous and oral antiovulatory activity. Provide evidence of homogeneity of the antagonists by paper or thin layerelectrophoresis, TLC, HPLC (or elution profile), and amino acid analysis. Determine the antiovulatory activity, s. c., of the antagonists in rats. Determine, by dose-related responses, the relative antiovulatory potency (activity) and duration of action using different acute dosage schedules.